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<br />Preprint from: Symposium on the Aquatic Resources Management <br />of the Colorado River Ecosystem. Nov. 16-19, <br />1981. Las Vegas, NV. Ann Arbor Science, Ann <br />Arbor, MI. (in press) <br /> <br />~ <br />a <br />w <br />w <br /> <br />:::0 <br />CJ <br /><:) <br />,--; <br /> <br />THE EFFECTS OF IMPOUNDMENTS ON <br />SALINITY IN THE COLORADO RIVER <br /> <br />~~ <br />d <br />~ <br />c <br /> <br />,L.J. Paulson <br />,J.R. Baker <br />Lake Mead Limnological Research Center <br />University of Nevada, Las Vegas <br /> <br />~~ <br /> <br />INTRODUCTION <br />, <br /> <br />The increase in salinity of our western rivers has been <br />identified as one of the most serious water quality problems <br />in the nation [1J. This is of special concern in the Colo-" <br />rado River,where salinity has increased from pristine levels <br />estimated at 380 mg/l [2J to present-day levels of 825 mg/l <br />at Imperial Dam [3,4J. Flow depletions, associated with <br />decreased runoff and increased evaporation and diversions, <br />coupled with high salt loading from natural and man-created <br />sources are considered the primary causes for rising salin- <br />ity in the river [5J. The urban and agricultural develop- <br />ment projected to occur in the basin through this century <br />,could' deplete flows by an additional 2 million acre-feet <br />:(2.5 x 109m9)/yr [4J. Salinity models indicate that deple- <br />tions of this magnitude will elevate total dissolved solids <br />concentrations (TDS) to 1150 mg/l at Imperial Dam. Since <br />this would have an enormous economic impact on municipal and <br />agricultural water uses [6J, salinity control prograins are <br />being implemented in the basin to maintain TDS at or below <br />the 1972 levels. <br />Historical data for the Colorado River, however, indi- <br />cate that TDS concentrations are not increasing as rapidly <br />as the models predict. Despite the extensive development and <br />large flow depletions that have already occurred in the ba- <br />sin, TDS concentrations in Grand Canyon and below Hoover Dam <br />have not changed appreciably since monitoring began [4J. <br />Water quality monitoring has recently shown that TDS concen- <br />trations throughout the Lower Colorado River Basin have been <br />decreasing since 1972. This is thought to be a transient <br />phenomenon caused by changes in flow patterns, salt routing <br />or possibly inundation of saline sources in the Upper Colo- <br />rado River Basin following completion of Lake Powell and <br />other impoundments during the 1960s [7J. This might also <br />reflect more permanent reductions in TDS due to changes in <br /> <br />1 <br /> <br />IO/I'1/?fL <br /> <br />I <br />